1. Field of the Invention
The present invention relates to systems for transporting fluids from one location to another. More particularly, the present invention relates to an apparatus to accommodate variations in component dimensions associated with temperature changes. Still more particularly, the present invention relates to expansion joints that connect fluid transport devices having fluids therein at significantly different temperatures. The present invention is an expansion joint that accommodates dimensional changes between adjacent fluid transport devices.
2. Description of the Prior Art
Expansion joints are used in many industries, including, but not limited to, the power generating industry. Expansion joints allow the relative movement of conduits (ducting, piping, etc.) used to control the flow of gases from one location to another. In the power generating industry in particular, the gases that are generated and that are to be diverted are very hot as they exit a turbine associated with a primary power generator. The hot turbine gases may either be exhausted directly via an exhaust stack or they may be directed to a secondary power generator. The secondary power generator may be used to recover a substantial portion of the thermal energy of the turbine exhaust gases. The gases generated by the turbine rise rapidly and place significant thermal stress on all components of a system in contact with those very hot gases. The expansion joint is designed to absorb thermal expansion in the exhaust ducting due to temperature changes. It is also designed to alleviate that thermal stress that comes from the transition from a "hot" fluid temperature zone to a "cold" fluid temperature zone. The expansion joint must therefore be designed specifically to accommodate a combination of all the above-noted duties.
U.S. Pat. No. 5,658,024 issued to Bachmann et al. describes the importance of the proper design of an expansion joint. The background section of the Bachmann patent is incorporated herein by reference. The Bachmann patent describes a new expansion joint design that eases the stress of any of the transitions associated with the connection between hot conduits having external insulation (a hot frame) and cold conduits having internal insulation (a cold frame). Of course, this can mean any transition wherein the temperature at the interior surface of one conduit is substantially different from the temperature at the exterior surface of an adjacent conduit.
In the power generating industry for example, it may be of importance to ensure that the exterior surface of a downstream conduit does not exceed a predetermined temperature. In some circumstances that temperature may be 65.degree. C. or less. At the same time, the interior surface of an adjacent upstream conduit in direct contact with the hot fluid being transported may be at 600.degree. C. or more. The prior Bachmann expansion joint provides one way of maintaining structural integrity in the coupling of the two adjacent conduits while also accounting for differentials in axial and lateral movement of those conduits as a function of temperature differentials. in particular, the prior Bachmann expansion joint includes a flexible material as an intermediary link between one end of the joint itself and the downstream conduit. The other end of the expansion joint is rigidly connected to the upstream conduit. A channel formed of one or more metal parts links the two ends of the expansion joint together. That channel includes a mouth within which fluid dwells.
The channeled Bachmann joint is designed with angled walls to form the mouth for capturing flowing fluid. Those angled walls are also intended to provide a geometry that is more tolerant of thermal stresses. Under most conditions, the angled-walls channel design is suitable to reduce sufficiently to acceptable levels the thermal stresses experienced in fluid flow conduits. However, the ability of the expansion joint element to perform at elevated temperatures is limited and, under some conditions, particularly those in which fluid temperatures are very high (600.degree. C. or more), it is advantageous for the exterior of an adjacent conduit to be at ambient temperature.
As noted, the prior Bachmann expansion joint includes a channeled section. That channeled section includes a metal-to-metal connection at its exterior surface, proximate to the exterior surface of the downstream conduit. The fluid within the mouth of the channeled section remains very hot. At the same time, the temperature at the exterior of the adjacent downstream internally-insulated conduit will be approximately at ambient. The flexible coupling that connects the exterior of the channeled section to the exterior of the downstream conduit is therefore subject to significant thermal stress due to the significant thermal gradient between its two contact points. Specifically, since the fluid within the mouth of the channeled section remains very hot, that end of the flexible coupling is also very hot. In fact, the temperature may exceed the temperature limitations of the flexible coupling material. Further, at transition areas of the channel, such as at the leg-to-base interfaces, there remains substantial thermal stress. That stress may cause weakening or failure of the expansion joint and, together with the flexible coupling's temperature limitation may cause potentially significant development of hazardous conditions caused by escaping fluid. Repair and maintenance costs may also be significant.
Therefore, what is needed is an expansion joint that accommodates differences in dimensional changes in adjacent fluid conduits. What is also needed is an expansion joint that is formed so that it is subject to minimal thermal distortion of the type that would cause its failure. Further, what is needed is an expansion joint design in which both ends of the expansion coupling are essentially at ambient temperature so as to ensure longevity of that coupling.